The subject of the invention is electrical battery management systems, and in particular the electrical battery management systems installed in and intended to propel a motor vehicle.
These batteries can be either recharged at electrical terminals when the vehicle is stopped, or recharged by recovering, through the electric motor, a portion of the kinetic energy of the vehicle when the latter decelerates. This is what is called regenerative braking.
It may be necessary to limit the power recovered and returned to the battery, for example so as not to compromise the operation of certain safety systems such as the ABS or ESP, as is described in the patent application WO 2008 040893.
It may also be necessary to limit the power returned to the battery in order not to damage the latter. Thresholds can then be imposed for the maximum current sent to the battery, or for the maximum voltage applied to the terminals of the battery.
Conventionally, a battery can be managed by an electronic control unit which monitors the maximum electrical power sent to the battery. This maximum electrical power can thus be linked to a maximum mechanical power authorized in recovery mode at the wheel level.
The limitations based only on the voltage threshold or only on a current intensity threshold do not make it possible to limit effects such as metal deposits in batteries of lithium ion type. Metallic lithium deposits can be produced at the negative electrode of the battery, in certain operating conditions in which the flow of Li+ ions arriving at the electrode is too great to allow the Li+ ions to be inserted into the graphite of the electrode. These Li+ ions then group together in the form of a metal deposit on the electrode, likely to create short circuits internal to the battery.
The patent application WO 2009 036444 proposes limiting this risk of lithium deposit by incorporating a reference electrode in each of the individual cells of the battery, and by monitoring the potential of the negative electrode relative to the reference electrode, so that it does not pass below a threshold potential of formation of the metallic lithium.
This solution is costly to apply because it assumes the insertion of reference electrodes in at least some of the cells of the battery. The system cost can become prohibitive if all the cells are equipped with a reference electrode, and may not be sufficiently reliable if only some of the cells are equipped.